Sea-level Rise, Coastal Flooding, and Storm Events

Treading Water: Tools to Help US Coastal Communities Plan for Sea Level Rise Impacts

Smith EA, Sweet W, Mitchell M, Domingues R, Weaver CP, Baringer M, Goni G, Haines J, J. Loftis D, Boon J, et al. Treading Water: Tools to Help US Coastal Communities Plan for Sea Level Rise Impacts. Frontiers in Marine Science [Internet]. 2019 ;6. Available from: https://www.frontiersin.org/articles/10.3389/fmars.2019.00300/full?utm_source=F-AAE&utm_medium=EMLF&utm_campaign=MRK_1023338_45_Marine_20190625_arts_A
Freely available?: 
Yes
Summary available?: 
No
Type: Journal Article

As communities grapple with rising seas and more frequent flooding events, they need improved projections of future rising and flooding over multiple time horizons, to assist in a multitude of planning efforts. There are currently a few different tools available that communities can use to plan, including the Sea Level Report Card and products generated by a United States. Federal interagency task force on sea level rise. These tools are a start, but it is recognized that they are not necessarily enough at present to provide communities with the type of information needed to support decisions that range from seasonal to decadal in nature, generally over relatively small geographic regions. The largest need seems to come from integrated models and tools. Agencies need to work with communities to develop tools that integrate several aspects (rainfall, tides, etc.) that affect their coastal flooding problems. They also need a formalized relationship with end users that allows agency products to be responsive to the various needs of managers and decision makers. Existing boundary organizations can be leveraged to meet this need. Focusing on addressing these needs will allow agencies to create robust solutions to flood risks, leading to truly resilient communities.

Protecting private properties from the sea: Australian policies and practice

Harvey N. Protecting private properties from the sea: Australian policies and practice. Marine Policy [Internet]. 2019 ;107:103566. Available from: https://www.sciencedirect.com/science/article/pii/S0308597X1830753X?dgcid=raven_sd_search_email
Freely available?: 
No
Summary available?: 
No
Approximate cost to purchase or rent this item from the publisher: 
US $35.95
Type: Journal Article

The vulnerability of private coastal properties is a global issue which has arisen largely because of a lack of understanding of coastal processes. In some countries where government authorities have a long history of funding private property protection works the sustainability and ethics of policies have been questioned together with debate over public rights and the rights of property owners. In Australia, where coast protection is a responsibility of state governments there is a variation in policies and legislation relating to planning approvals for coast protection works in front of private properties. This paper examines the different Australian policies and uses examples from practice to illustrate these differences. The paper notes a wide variation in the ratio of public versus private funding which does not always match the relative proportion of benefit gained from protection works. The paper concludes that there is a complex pattern of individual state-based coastal policies, legislation and guidelines related to protection of private coastal properties. These have an underlying principle that protection works must be fully assessed in the context of effects on the adjacent coast and neighbouring properties. In reality, this requires a detailed understanding of coastal processes, particularly sediment movement, within broad sections of the coast referred to as sediment cells. Such an integrated approach has been introduced to some state-based Australian coastal legislation and strategies.

Linking management planning for coastal wetlands to potential future wave attenuation under a range of relative sea-level rise scenarios

Hijuelos ACommagere, Dijkstra JT, Carruthers TJB, Heynert K, Reed DJ, van Wesenbeeck BK. Linking management planning for coastal wetlands to potential future wave attenuation under a range of relative sea-level rise scenarios Chapman MGeraldine. PLOS ONE [Internet]. 2019 ;14(5):e0216695. Available from: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0216695
Freely available?: 
Yes
Summary available?: 
No
Type: Journal Article

Understanding changes in wave attenuation by emergent vegetation as wetlands degrade or accrete over time is crucial for incorporation of wetlands into holistic coastal risk management. Linked SLAMM and XBeach models were used to investigate potential future changes in wave attenuation over a 50-year period in a degrading, subtropical wetland and a prograding, temperate wetland. These contrasting systems also have differing management contexts and were contrasted to demonstrate how the linked models can provide management-relevant insights. Morphological development of wetlands for different scenarios of sea-level rise and accretion was simulated with SLAMM and then coupled with different vegetation characteristics to predict the influence on future wave attenuation using XBeach. The geomorphological context, subsidence, and accretion resulted in large predicted reductions in the extent of vegetated land (e.g., wetland) and changes in wave height reduction potential across the wetland. These were exacerbated by increases in sea-level from +0.217 m to +0.386 m over a 50-year period, especially at the lowest accretion rates in the degrading wetland. Mangrove vegetation increased wave attenuation within the degrading, subtropical, saline wetland, while grazing reduced wave attenuation in the temperate, prograding wetland. Coastal management decisions and actions, related to coastal vegetation type and structure, have the potential to change future wave attenuation at a spatial scale relevant to coastal protection planning. Therefore, a coastal management approach that includes disaster risk reduction, biodiversity, and climate change, can be informed by coastal modeling tools, such as those demonstrated here for two contrasting case studies.

Assessing Morphologic Controls on Atoll Island Alongshore Sediment Transport Gradients Due to Future Sea-Level Rise

Shope JB, Storlazzi CD. Assessing Morphologic Controls on Atoll Island Alongshore Sediment Transport Gradients Due to Future Sea-Level Rise. Frontiers in Marine Science [Internet]. 2019 ;6. Available from: https://www.frontiersin.org/articles/10.3389/fmars.2019.00245/full?utm_source=F-AAE&utm_medium=EMLF&utm_campaign=MRK_993741_45_Marine_20190521_arts_A
Freely available?: 
Yes
Summary available?: 
No
Type: Journal Article

Atoll islands’ alongshore sediment transport gradients depend on how island and reef morphology affect incident wave energy. It is unclear, though, how potential atoll morphologic configurations influence shoreline erosion and/or accretion patterns, and how these relationships will respond to future sea-level rise (SLR). Schematic atoll models with varying morphologies were used to evaluate the relative control of individual morphological parameters on alongshore transport gradients. Incident wave transformations were simulated using a physics-based numerical model and alongshore erosion and accretion was calculated using empirical formulae. The magnitude of the transport gradients increased with SLR: initial erosion or accretion patterns intensified. Modeled morphologic parameters that significantly influenced alongshore transport were the atoll diameter, reef flat width, reef flat depth, and island width. Modeled atolls with comparably small diameters, narrow and deep reef flats with narrow islands displayed greater magnitudes of erosion and/or accretion, especially with SLR. Windward island shorelines are projected to accrete toward the island’s longitudinal ends and lagoon due to SLR, whereas leeward islands erode along lagoon shorelines and extend toward the island ends. Oblique island, oriented parallel to the incident deepwater wave direction, shorelines are forecast to build out leeward along the reef rim and toward the lagoon while eroding along regions exposed to direct wave attack. These findings make it possible to evaluate the relative risk of alongshore erosion/accretion on atolls due to SLR in a rapid, first-order analysis.

Linking management planning for coastal wetlands to potential future wave attenuation under a range of relative sea-level rise scenarios

Hijuelos ACommagere, Dijkstra JT, Carruthers TJB, Heynert K, Reed DJ, van Wesenbeeck BK. Linking management planning for coastal wetlands to potential future wave attenuation under a range of relative sea-level rise scenarios Chapman MGeraldine. PLOS ONE [Internet]. 2019 ;14(5):e0216695. Available from: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0216695
Freely available?: 
Yes
Summary available?: 
No
Type: Journal Article

Understanding changes in wave attenuation by emergent vegetation as wetlands degrade or accrete over time is crucial for incorporation of wetlands into holistic coastal risk management. Linked SLAMM and XBeach models were used to investigate potential future changes in wave attenuation over a 50-year period in a degrading, subtropical wetland and a prograding, temperate wetland. These contrasting systems also have differing management contexts and were contrasted to demonstrate how the linked models can provide management-relevant insights. Morphological development of wetlands for different scenarios of sea-level rise and accretion was simulated with SLAMM and then coupled with different vegetation characteristics to predict the influence on future wave attenuation using XBeach. The geomorphological context, subsidence, and accretion resulted in large predicted reductions in the extent of vegetated land (e.g., wetland) and changes in wave height reduction potential across the wetland. These were exacerbated by increases in sea-level from +0.217 m to +0.386 m over a 50-year period, especially at the lowest accretion rates in the degrading wetland. Mangrove vegetation increased wave attenuation within the degrading, subtropical, saline wetland, while grazing reduced wave attenuation in the temperate, prograding wetland. Coastal management decisions and actions, related to coastal vegetation type and structure, have the potential to change future wave attenuation at a spatial scale relevant to coastal protection planning. Therefore, a coastal management approach that includes disaster risk reduction, biodiversity, and climate change, can be informed by coastal modeling tools, such as those demonstrated here for two contrasting case studies.

Accounting for spatial patterns in deriving sea-level rise thresholds for salt marsh stability: More than just total areas?

Wu W. Accounting for spatial patterns in deriving sea-level rise thresholds for salt marsh stability: More than just total areas?. Ecological Indicators [Internet]. 2019 ;103:260 - 271. Available from: https://www.sciencedirect.com/science/article/pii/S2212041618305898
Freely available?: 
No
Summary available?: 
No
Approximate cost to purchase or rent this item from the publisher: 
US $35.95
Type: Journal Article

Ecological threshold is an important concept to indicate the boundary of alternate states of ecosystems driven by environmental conditions and to facilitate evaluation of ecosystem resilience. Sea-level rise (SLR) thresholds for the stability of salt marshes, if studied in two dimensions, are generally derived based on total areas without systematic accounting for spatial patterns related to edges, shapes, and contagions of patches. As these spatial patterns are potentially important for functions and ecosystem services of salt marshes and they are likely to be impacted by SLR in a different way from the total areas, it is necessary to study SLR thresholds based on these spatial patterns to obtain a more comprehensive understanding of salt marsh resilience to SLR. This research compares the SLR thresholds based on these spatial patterns of salt marshes to those based on total areas alone across different spatial resolutions.

The spatial patterns of salt marshes were quantified by 26 commonly used landscape metrics, predicted from a mechanistic wetland change model. At spatial resolutions of 2–100 m, SLR thresholds were first derived using individual landscape metrics and then the first principal component that explained >80% of total variance of these metrics showing threshold responses to SLR. In order to separate the effect of spatial configuration from composition, a neutral model which simulated the same amount of salt marsh change as the mechanistic model but at the random locations was applied. The SLR thresholds were derived based on the simulations from the neutral model and compared to those from the mechanistic model.

The results show that total area-based SLR thresholds do not comprehensively represent salt marshes’ resilience to SLR. Particularly, I find 1) the derived SLR thresholds vary from 7.29 to 11.12 mm/yr for 2100 based on landscape metrics used, 2) the SLR threshold based on the first principal components (7.99 mm/yr) is smaller than that based on the total area only (8.40 mm/yr), 3) the SLR thresholds are scale dependent, and 4) the spatial configuration’ effect on SLR thresholds is smaller for smaller salt marsh areas compared to larger salt marsh areas.

This study highlights the need to account for different spatial patterns of salt marshes and apply wetland maps with a spatial resolutions of 30 m or finer in deriving SLR thresholds, as using total areas alone or coarser-resolution maps may provide a biased interpretation that salt marshes are more resilient to SLR than they actually are.

Disaster on the Horizon: The Price Effect of Sea Level Rise

Bernstein A, Gustafson MT, Lewis R. Disaster on the Horizon: The Price Effect of Sea Level Rise. Journal of Financial Economics [Internet]. In Press . Available from: https://www.sciencedirect.com/science/article/pii/S0304405X19300807
Freely available?: 
No
Summary available?: 
No
Approximate cost to purchase or rent this item from the publisher: 
US $39.95
Type: Journal Article

Homes exposed to sea level rise (SLR) sell for approximately 7% less than observably equivalent unexposed properties equidistant from the beach. This discount has grown over time and is driven by sophisticated buyers and communities worried about global warming. Consistent with causal identification of long-horizon SLR costs, we find no relation between SLR exposure and rental rates and a 4% discount among properties not projected to be flooded for almost a century. Our findings contribute to the literature on the pricing of long-run risky cash flows and provide insights for optimal climate change policy.

Dual wave farms for energy production and coastal protection under sea level rise

Rodriguez-Delgado C, Bergillos RJ, Iglesias G. Dual wave farms for energy production and coastal protection under sea level rise. Journal of Cleaner Production [Internet]. In Press . Available from: https://www.sciencedirect.com/science/article/pii/S0959652619307474
Freely available?: 
No
Summary available?: 
No
Approximate cost to purchase or rent this item from the publisher: 
US $39.95
Type: Journal Article

Climate change is poised to exacerbate coastal erosion. Recent research has presented a novel strategy to tackle this issue: dual wave farms, i.e., arrays of wave energy converters with the dual function of carbon-free energy generation and coastal erosion mitigation. However, the implications of sea level rise – another consequence of climate change – for the effectiveness of wave farms as coastal defence elements against shoreline erosion have not been studied so far. The objective of this work is to investigate how the coastal defence performance of a dual wave farm is affected by sea level rise through a case study (Playa Granada, southern Iberian Peninsula). To this end, a spectral wave propagation model, a longshore sediment transport formulation and a one-line model are combined to obtain the final subaerial beach areas for three sea level rise scenarios: the present situation, an optimistic and a pessimistic projection. These scenarios were modelled with and without the wave farm to assess its effects. We find that the dual wave farm reduces erosion and promotes accretion regardless of the sea level rise scenario considered. In the case of westerly storms, the dual wave farm is particularly effective: erosion is transformed into accretion. In general, and importantly, sea level rise strengthens the effectiveness of the dual wave farm as a coastal protection mechanism. This fact enhances the competitiveness of wave farms as coastal defence elements.

Coastal flooding from wave overtopping and sea level rise adaptation in the northeastern USA

Xie D, Zou Q-P, Mignone A, MacRae JD. Coastal flooding from wave overtopping and sea level rise adaptation in the northeastern USA. Coastal Engineering [Internet]. In Press . Available from: https://www.sciencedirect.com/science/article/pii/S0378383917305653
Freely available?: 
No
Summary available?: 
No
Approximate cost to purchase or rent this item from the publisher: 
US $35.95
Type: Journal Article

In the northeastern United States, flooding arising from wave overtopping poses a constant threat to coastal communities during storm events. The purpose of this study is to construct a novel integrated atmosphere-ocean-coast modeling framework based on the coupled tide, surge and wave model, ADCIRC-SWAN, to assess risk and facilitate coastal adaptation and resilience to flooding in a changing climate in this region. The integrated modeling system was validated against the field observations of water level, wave height and period during the January 2015 North American blizzard. Water level measurements by a sensor in the Avenues Basin behind the Seawall in Scituate, Massachusetts were combined with the basin volume determined by the USGS LIDAR data to verify the model predictions of wave overtopping volume. At the storm peak, the significant wave height was increased by 0.7 m at the coast by tide and surge. The wave setup along the coast varied from 0.1 m to 0.25 m depending on the coastline geometry. The interaction between tide-surge and waves increased the wave overtopping rate by five folds mainly due to increased wave height at the toe of the seawall. The wave overtopping discharge would approximately double in an intermediate sea level rise scenario of 0.36 m by 2050 for a storm like the January 2015 North American blizzard. The wave overtopping discharge would increase by 1.5 times if the seawall crest elevation was raised by the same amount as sea level rise. An increase of 0.9 m in the seawall crest elevation is required to bring the wave overtopping discharge to the current level under a 0.36 m sea level rise scenario, primarily due to larger waves arriving at the seawall without breaking in the presence of larger water depth.

Assessing Beach and Dune Erosion and Vulnerability Under Sea Level Rise: A Case Study in the Mediterranean Sea

Enríquez AR, Marcos M, Falqués A, Roelvink D. Assessing Beach and Dune Erosion and Vulnerability Under Sea Level Rise: A Case Study in the Mediterranean Sea. Frontiers in Marine Science [Internet]. 2019 ;6. Available from: https://www.frontiersin.org/articles/10.3389/fmars.2019.00004/full
Freely available?: 
Yes
Summary available?: 
No
Type: Journal Article

In this study, we estimate the shoreline retreat, the vulnerability and the erosion rates of an open beach-dune system under projected sea level rise (SLR) and the action of wind-waves (separately and in combination). The methodology is based on the combination of two state-of-the-art numerical models (XBeach and Q2D-morfo) applied in a probabilistic framework and it is implemented in an open sandy beach in Menorca Island (Western Mediterranean). We compute the shoreline response to SLR during the 21st century and we assess the changing impacts of storm waves on the aerial beach-dune system. Results demonstrate the relevant role that the beach backshore features, such as the berm, play as coastal defense, reducing the shoreline retreat and dune vulnerability rates in the near-term (a few decades ahead) and highlighting the importance of simulating the beach morphodynamic processes in coastal impacts assessments. Our findings point at SLR as the major driver of the projected impacts over the beach-dune system, leading to an increase of ∼25% of the volume eroded due to storm waves by the end of the century with respect to present-day conditions.

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